Previously, we developed radioimmunoassays for the MM and BB isoenzymes of creatine kinase in human serum. Currently we are investigating the clinical usefulness of these assays by measuring isoenzyme levels in serum and cerebro-spinal fluid from patients with schizophrenia, in the serum of patients with neuromuscular diseases, prostatic and other cancers, myocardial injury, and in the serum of patients undergoing cardiac surgery. The assay for the BB isoenzyme seems particularly useful. Elevations in CK-BB occur in neuromuscular diseases, myocardial infraction, prostatic and several other cancers, as well as following cardiac surgery.